The present invention relates to multi-axis machines for positioning a machine tool, such as a drill, riveter, or the like, relative to a structure or workpiece on which work operations are to be performed by the tool. The invention relates more particularly to a portable multi-axis positioning machine that attaches to a structure or workpiece being operated upon such that positioning and orientation of the machine are set by physically indexing the machine to features on the workpiece.
The current state of the art in numerically controlled drilling or machining of large structures such as air frame components involves the use of large fixed-base multi-axis machines that are mounted upon a foundation and typically have a large work envelope for accessing all parts of the largest structures that are expected to be worked on. These machines are quite expensive, and also have a number of operational limitations. For instance, the machines have only one spindle and hence can perform work operations on only one location of the structure at a time. Because of the large work envelope, it is difficult for the machines to hold close tolerances over the entire range of movement capabilities in all axes of the machine. The machines also require permanent floor space and require the structure that is to be processed to be brought to the machine. The machine must then xe2x80x9cacquirexe2x80x9d the structure by probing known features of the structure so that the machine""s controller knows where the structure is located relative to the machine. Typically a xe2x80x9cbest fitxe2x80x9d calculation is made based on the probe data to achieve as close a fit as possible between the numerical nominal definition of the structure and the probe data. Once this process is completed, work operations can begin. During machining, it is frequently necessary to employ further aids to properly orient the machine relative to the structure, such as laser alignment systems or the like. It is also common for recalibration of the machine relative to the structure to be required during work operations.
The need to probe and calibrate the machine to the workpiece one or more times during work operations has a significant negative impact on the overall efficiency and cost of the process. Furthermore, the need to bring the workpiece to the machine means that nonproductive transit time is incurred in the process.
The present invention seeks to improve upon the situation described above by providing a portable multi-axis machine. Probing of the workpiece to be machined and xe2x80x9cbest fitxe2x80x9d calibrating of the numerical control to the workpiece are eliminated by physically indexing the machine to the workpiece by engaging the machine with fittings or other features in known locations on the workpiece. Once the machine is engaged with the fittings or features, a coordinate system based in the machine is automatically in a known location and orientation relative to the workpiece. Moreover, because the machine is portable, the workpiece can remain in a fixed location. The machine is relatively small in size and weight, such that more than one such machine can work on different portions of the workpiece at the same time, thereby improving productivity.
To these ends, a multi-axis machine in accordance with one preferred embodiment of the invention comprises a frame structured and arranged to engage a surface of the workpiece and to engage reference features on the workpiece so as to position and orient the frame relative to the workpiece, a working module operable to hold a tool in a tool holder and manipulate the tool for performing a work operation on the workpiece, and a pair of 2-axis positioning devices. A first 2-axis positioning device is mounted on the frame and a second 2-axis positioning device is mounted on the frame spaced from the first 2-axis positioning device, each 2-axis positioning device being operable to translate independently along each of two translational axes. The working module is connected between the 2-axis positioning devices such that the working module is translated by synchronous translational movements of the 2-axis positioning devices and the working module is rotated about at least one axis by differential translational movements of the 2-axis positioning devices.
Preferably, the frame has a workpiece-engaging side structured and arranged to engage a surface of the workpiece with a three-point contact therebetween such that the frame stably engages surfaces of varying and complex contour and the three-point contact establishes approximate normality between a Z-axis of the machine and the surface of the workpiece. Additionally, the positioning devices preferably comprise XY positioning devices operable to translate the respective end of the working module independently along each of two translational X and Y axes defining an XY plane parallel to that of the other XY positioning device and spaced therefrom along the Z axis. The XY positioning devices are operable to translate along the X and Y axes independently of each other in their respective XY planes. Accordingly, for many different workpiece surface contours, the machine can achieve normality between the axis of the tool holder and the workpiece surface at any point within a working envelope of the machine.
The machine indexes to the workpiece in preferred embodiments of the invention by a pair of index cylinders mounted on the frame with their axes parallel to the Z-axis of the machine. A pair of tool balls or similar spherical fittings are rigidly mounted on the workpiece in known locations thereof so as to serve as reference points. The tool balls are received into the index cylinders of the machine, thereby indexing the machine to the workpiece. One of the index cylinders is mounted in a fixed location on the frame, and the other index cylinder is slidable for adjusting the spacing between the index cylinders.
The working module is coupled with the positioning devices by rotatable couplings such as spherical bearings or the like. In one embodiment, the working module is mounted on the first positioning device by a gimbal arrangement enabling the working module to pivot about first and second rotational axes that are perpendicular to the spindle axis of the working module, and the second positioning device is coupled with the working module via a spherical bearing accommodating the pivotal movements of the working module. The pivotal movements of the working module are produced by appropriate control of the positioning devices to provide differential movements between the two positioning devices along the X and/or Y axes. Because the working envelope of the machine is relatively small, the required range of pivotal movement for maintaining normality of the spindle axis to the workpiece surface at any point in the working envelope is relatively small (e.g., about 30 degrees or less) for workpieces having relatively large radii of curvature as is true for components of air frames such as wing and fuselage sections. Accordingly, there is no need to provide the large range of rotational motion about the rotational axes that is commonly employed in large fixed-base multi-axis machines.
The first XY positioning device preferably comprises a first pair of spaced X-axis rails mounted proximate the workpiece-engaging side of the frame. A first X-axis drive arrangement drives the working module along the X-axis rails of the first positioning device. The second positioning device comprises at least one X-axis rail mounted on the side of the frame opposite the workpiece-engaging side. A remote end of the working module is driven along the rail of the second positioning device by a second X-axis drive arrangement that is controllable independently of the first X-axis drive arrangement. The working module is slidable along a first pair of Y-axis rails that extend between and are slidably connected to the first pair of X-axis rails, and is driven in the Y direction by a first Y-axis drive arrangement. The remote end of the working module is slidable along at least one second Y-axis rail that is slidably connected to the second X-axis rail, and is driven in the Y direction by a second Y-axis drive arrangement that is controllable independently of the first Y-axis drive arrangement.
In a preferred embodiment of the invention, the machine includes a plurality of vacuum devices mounted on the workpiece-engaging side of the frame for engaging the workpiece and urging the machine against the workpiece by vacuum so as to stabilize the machine.